Freezing and multi-stage freezing method using gas as refrigerant

Abstract

A freezing method using a gas as a refrigerant, comprising: step 1: using a colorless, tasteless, and non-toxic liquid gas or supercritical gas as a refrigerant for freezing; step 2: immersing a product to be frozen in the liquid gas or the supercritical gas until the center temperature of the product to be frozen reaches the temperature of a freezing stage; and step 4: taking out the product to be frozen and transferring it to a frozen storage low temperature environment for storing. A multi-stage freezing method using a gas as a refrigerant, comprising: step 1: dividing the freezing process for a product to be frozen into at least two freezing stages; step 2: sequentially performing freezing operations corresponding to each of the freezing stages on the product to be frozen; and step 3: transferring, after balancing the pressure of the product to be frozen with the atmospheric pressure, the product to be frozen to the frozen storage low temperature environment for storing.

Description

BACKGROUND OF THE INVENTION[0001]The present invention relates to the technical field of freeze storage, and more particularly relates to freezing and multi-stage freezing method using gas as refrigerant.[0002]Immersion freezing employs a chiller to chill freezing fluid, and food will then be immersed into the freezing fluid to get frozen. The freezing fluid is also called refrigerant. Immersion freezing is a very effective kind of freezing method that possesses many advantages that other freezing methods do not possess. Immersion freezing has at least a few distinctive advantages as described below:[0003]1. Quick freezing. Thermal conductivity of air in room temperature is 0.024 W / (M.K). Most kinds of liquid have a thermal conductivity of 0.116-0.628 W / (M.K), which is 5-26 times the thermal conductivity of air. Freezing by means of forced convection of air uses air in normal pressure as a freezing agent. By contrast, the freezing agent of immersion freezing is freezing liquid (refr...

AI Technical Summary

Benefits of technology

The present invention provides a freezing method using gas as the refrigerant that does not leave any residue in the food products, does not change their flavor, and maintains the original quality of the refrigerant after immersion freezing. The method uses liquefied or supercritical gas as the refrigerant, and during the freezing process, the pressure is maintained. This technique has the advantage of accurately controlling the freezing temperature of the food product using temperature-controlled refrigeration apparatus. Additionally, the refrigerant naturally vaporizes after pressure release, which makes it easy to separate from impurities and maintain the quality of the refrigerant. The method also uses liquefied or supercritical gas of different temperatures to perform multi-stage freezing, which reduces the temperature difference between the food product and the refrigerant, preventing the food product from cracking during rapid and super cold immersion freezing.

Problems solved by technology

Therefore, when compared with the former, the latter has a very quick freezing speed requiring a very short time to complete freezing.

However, since these refrigerants currently used in immersion freezing are liquids in normal temperature and normal pressure, at least the following several problems exist:

On one hand, during immersion of the food products, some refrigerants will inevitably be transferred to the food products, and these liquid form of refrigerants are difficult to volatilize and are therefore left permanently in the food products (some alcoholic type of refrigerants are volatile yet they may somehow react with the frozen products and change the flavor of the products); as such, these refrigerants may change the flavor of the frozen food products and may even cause the amount of additives exceeding a prescribed limit.

Even if the food products are first packed and then indirectly immersed in the refrigerants, it is possible that in actual practice, the packaging may be damaged and thus allowing the refrigerants to contact the food products; besides, this method increases the freezing cost.

On the other hand, during immersion freezing, some food product substances will inevitably be transferred to the refrigerants, and these substances will be dissolved in the refrigerants and thus very difficult to be separated from the refrigerants.

Therefore, each time after immersion freezing, quality of the refrigerants decreases, and this leads to a low rate of recycling the refrigerants, which in turns greatly increases the freezing cost.

Some irregular or sharp food products (such as shrimps, crabs etc.) may easily damage the packaging that separates the food products from the refrigerants.

Therefore, these food products are not suitable for indirect immersion freezing.

Some small food products (such as cherries, lychees, longans and peas etc.) are difficult to be packaged individually or may otherwise greatly increase the cost; however, a plural number of small food products packaged in a single packaging may easily result in uneven freezing effect.

Therefore, indirect immersion freezing of these small food products does not achieve good freezing effect.

However, high concentration of salts may easily lead to corrosion of equipment.

Ethanol is volatile, which can reduce the effectiveness of the refrigerants, and ethanol is also a hazardous substance that is flammable and explosive, thus it poses a potential risk against safety production.